Introduction: Air Purifier

Picture of Air Purifier

This is a powerfull air purifier which use G4 and F7 filter. The HEPA F7 filter is sufficient to stop pollens. This air purifier is intended to clean the air of a big room during allergic periods.

Step 1: Hardware

Picture of Hardware

The fan as been chosen from the requisites of the filters. The filters are rated for a amount of air flow and oppose some resistance. When they get dirty, the resistance increase as well. The fan is powerfull enough to deliver air pressure up to the max rated by the filters.

I made a mistake when buying the fan. It is no dimable. It's either full power (and noisy) or off.

The fan is inside a crate, creating a depression behind the filters and the exhaust is located one one side.

Step 2: Building the Crate

Picture of Building the Crate

The fan is fixed inside a crate. It's made with laser cutted 5mm plywood. Because the fan is quite heavy, and a rest for the filters is needed, the bottom of the crate is reinforced with wood pieces. Carrefully cuted with the same length, it wasn't correctly pushed to the maximum. I used wood paste to fill the gape and avoid any air leaking possibility.

Step 3: Exhaust

Picture of Exhaust

Since I used some foam to try to reduce vibrations and noise, it wasn't very easy to cut the exhaust a the rigth place with the laser cutting machine. I did it with a drill. Not very clean but it won't be visible.

Step 4: Fixing the Fan

Picture of Fixing the Fan

Every contact surface of the fan is using foam in a desperate attempt to lower the noise. Because the fan is quite heavy, it was necessary to have two points of contact. A laser cutted piece of wood is used for the exhaust. The bolds are pointing outside, I kept them like this because I will build a silencer for the exhaust and th bolds are very usefull to fix this extension later.

Step 5: Sealing the Crate

Picture of Sealing the Crate

To ensure that the low pressure chamber gets air through the filter, I used some putty. The electric cord is also a weak point. I drilled a hole smaller than the diameter of the cord and slightly enlarge it with a file. It fits perfectly.

Step 6: Electric Box

Picture of Electric Box

The electric box is glued on the back of the crate. Since the fan is not dimable, I used a simple on/off switch. Some velcro band are used ton fix the electric cord. I drilled some holes in case of heating issues but I did it on the sides of the box which is not the best choice .

Step 7: Inserting the Filter

Picture of Inserting the Filter

The H7 filter is seated on a wooden square which is seated on the wooden pieces that also give more strength to the crate. Some ruber band sold to seal windows or doors is used to seal the sides of the H7 filter.

The last filter is just pushed inside the crate. The size is the same. Friction easily keep the filter in place.

To close the crate a more or less pretty grid has been laser cutted. It offers too much air resistance and needs a real fixing system.


TheArduinoGuy (author)2018-01-15

Why can it not be controlled with PWM ?

Luk--- (author)TheArduinoGuy2018-01-15

I have very limited knoledge in electricity and none in electronics (I've just searched PWM).

I guess the fan has an induction motor. It was featured with a control device (the black thing in the electrical box).

Maybe it is controllable by PWM but it's far from my skills for now.

Thank you for your concern.

diy_bloke (author)Luk---2018-01-15

I understand it is being fed from the mains grid. Thus cannot be fed bij PWM.

Tou could use a TRIAC to control it by phasecutting. That will most likely work, though TRIACs are not specifically suited to regulate inductive loads

JoãoP142 (author)diy_bloke2018-01-19

Unless you use a capacitor in parallel with the fan to nullify the induction. Or to at least bring the potential factor close to 1.

JoãoP142 (author)2018-01-18

You can't dim it? Have you tried to use a system with a TRIAC together with a DIAC?

JoãoP142 (author)JoãoP1422018-01-19

Sorry for the double post.

Dominguez alejandro (author)2018-01-19


Si Ud agrega un generador de Ozono, agregará una función muy especial que es la de ionizar el ambiente con iones negativos. La plaqueta es muy simple, consta de 40 diodos tipo BY (Fast Diode) y igual cantidad de condensadores, todos colocados en una Pcb y alimentada a 220 ó 110 volts VAC..

Con este circuito Ud beneficiará y optimizará el ánimo y rendimiento de las personas ya que los iones negativos predispone el buen ánimo a los seres humanos. El costo del armado de la Pcb es muy bajo y los beneficios muy buenos.

Cordiales saludos desde Argentina

JoãoP142 (author)2018-01-18

You can't dim it? Have you tried using a controlling system with a TRIAC together with a DIAC?

zonkerharris (author)2018-01-18

Most home fans or air filters have fans which are powered from the AC wall socket power, and may have 1, 2, or 3 speeds selected with a switch. But, you can get DC powered fans (recycled from computer power supplies, for example) which have Tachometer and PWM speed control wires. Such fans have red, black, yellow and blue wires.

An Arduino (or other embedded controller) can use a PWM output to control the speed. This could be as simple as using an ATtiny85 to read an analog input from a potentiometer between 5v and ground, and map that reading to the PWM output pin, and you'd have a simple speed control.

The solution above, with a DC fan, combined with these construction ideas, might be a good fit. Maybe adding a barometric sensor inside the box could tell you when the filter is getting clogged (and the fan is working harder to pull the air), or use the tachometer reading at various PWM settings (compare no filter, new filter to get readings) and then set comparisons in the code to light an LED to change the filter. That may be a fun weekend project!

d_talker (author)2018-01-16

Hi! What about noize? What about PM 2.5?

Luk--- (author)d_talker2018-01-16

It's very loud. The fan constructor is announcing 70db. I strongly recommend to chose a variable fan. I clearly made a mistake on this.

RumblePirate (author)Luk---2018-01-16

I've tried a lot with air purifier ides, but the noise from the fan is always the issue at hand. in order to create proper suction n blower effect with the addition of filters, it becomes major issue.. thats me so far

SimpleDaze (author)2018-01-16

I don’t have a laser cutter(yet) is there a possibility of me buying the laser cut pieces from you?

Luk--- (author)SimpleDaze2018-01-16

I'm using the laser cutting machine from a fablab so it's not intended for commercial use. I'm also in France, so it could cost you some money just for sending it. There is some online commercial services that might help. I know (but didn't test) I'm pretty sure there is other companies alike. If you choose this solution, you may print on paper and cut it by hand first to be sure that you pieces are adjusting correctly.

jim.buchanan.165 (author)2018-01-15

Great project! It looks better than the one I built about 3 years ago. Mine uses a box fan (the sort of thing you use to cool rourself off on hotdays) instead of a centrifigul blower. That automatically gave me 3 speeds. It uses a square furnace filter (I normally use a HEPA filter)

Luk--- (author)jim.buchanan.1652018-01-16

It's a bit crude but it's a smart hacking for existing equipments. At the begning, I was thinking to use a radial fan as well to build a dual purpose machine : cleaning air and using a strong radial fan to force air circulation inside my flat (one side is very hot in summer, the other side si cool. I choose a centrifugal fan because radial ones are known to deliver less pressure than centrifugal ones. It was not enough with my filters. I would be enough for lighter filters I guess.

MishaL1 (author)jim.buchanan.1652018-01-16

Nice ! I did the same with box fan, but just attached filter straight on fan. Was very helpful during renovations to remove a lot of dust from the air !

psikelly (author)2018-01-16

Thank you so much. I now have an affordable solution to deal with kitty litter dust.

Dr_Stupid (author)2018-01-16

Purifier? not exactly, that's an air filter.

ar_caver (author)Dr_Stupid2018-01-16

HEPA filters can remove mold spores and bacteria, so they are purifying the air to that extent. If you want to remove viruses then you could add UV light or an ozone generator. I believe this qualifies as an air purifier. I think this is a nice project that could be very benificial for many people.

LucindaG6 (author)Dr_Stupid2018-01-16

What exactly does an air filter do if not purify "remove contaminents from" the air. Purifiers don't ever produce pure air. They only try, like his does! Have a nice day!

arrowfire (author)2018-01-15

Do you plan to post a list of materials along with dimensional plans on how to build it? Thanks!

Luk--- (author)arrowfire2018-01-15

I'll do it in a few days but there it is a simple design with dimensions adapted to the filters. I guess you would have to change it's dimension if you buy filters of a different shape.

ljhopkins (author)2018-01-15

where did you get your motor/blower?

Luk--- (author)ljhopkins2018-01-15

I bought it on ebay from a british company :

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